Class: Senior Secondary School 1 (SS1 / SSS 1)
Term: 3rd Term
Week: 3
Age: 15 years
Duration: 45 minutes
Subject: Electrical Installation and Maintenance Work
Curriculum Theme: Technology
Previous Lesson: Fuses: Types, IEE Regulation and Key Terms.
Topic: CIRCUIT BREAKER
Subject Matter: Meaning of circuit breaker, functions of circuit breaker, types of circuit breakers, current operated circuit breaker, voltage operated circuit breaker.

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Define a circuit breaker.
State at least three functions of a circuit breaker.
List different types of circuit breakers.
Explain the operation of current operated and voltage operated circuit breakers.

Affective Domain:

Appreciate the importance of circuit breakers in electrical safety.
Show interest in learning about electrical protection devices.

Psychomotor Domain:

Identify different types of circuit breakers when shown.
Differentiate between a current operated and a voltage operated circuit breaker.

Participate actively in discussions about electrical safety.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Electrical Installation and Maintenance Work.
State Unified Scheme of Work for Senior Secondary School Electrical Installation and Maintenance Work.
Electrical Installation Technology for Senior Secondary Schools.

Instructional Materials

The teacher will teach this lesson with the aid of:

Samples of current operated circuit breakers.
Samples of voltage operated circuit breakers.
Charts showing diagrams of various circuit breakers.
Whiteboard and markers.

Rationale for the Lesson

This lesson helps pupils understand how circuit breakers protect electrical circuits and appliances from damage caused by overcurrents or short circuits. Knowing about circuit breakers enables pupils to appreciate their role in ensuring safety in homes and other electrical installations.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of electrical circuits, current, voltage, and the concept of fuses from previous lessons.

Lesson Content/Board Summary

Circuit Breaker

Meaning of Circuit Breaker

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by an overcurrent or short circuit. Its basic function is to detect a fault condition and interrupt current flow.

Functions of Circuit Breakers

The following are functions of circuit breakers:

They protect electrical appliances from damage due to overcurrents.
They prevent electrical fires by tripping when there is a fault.
They protect people from electric shock by disconnecting the power supply during fault conditions.
They can be manually reset after a fault is cleared, unlike fuses which need replacement.
They provide a means of manually switching off a circuit for maintenance or safety.

Types of Circuit Breakers

Circuit breakers are generally classified based on their operating mechanism and application. Common types include:

Miniature Circuit Breakers (MCB)
Moulded Case Circuit Breakers (MCCB)
Residual Current Devices (RCD) / Earth Leakage Circuit Breakers (ELCB)
Air Circuit Breakers (ACB)
Vacuum Circuit Breakers (VCB)
Sulphur Hexafluoride Circuit Breakers (SF6 CB)

Based on the detection method, two common types are:

Current Operated Circuit Breaker
Voltage Operated Circuit Breaker

Current Operated Circuit Breaker

A current operated circuit breaker detects faults by monitoring the current flowing through the circuit. When the current exceeds a predetermined safe limit (e.g., due to an overload or short circuit), the magnetic or thermal tripping mechanism activates, causing the breaker to open the circuit.

These are commonly used for overcurrent protection in homes and industries.

Voltage Operated Circuit Breaker

A voltage operated circuit breaker (often an older type of Earth Leakage Circuit Breaker – ELCB) detects faults by monitoring the voltage difference between the main conductor and the earth. If a dangerous voltage appears on an earthed metal part due to an insulation fault, the breaker trips, disconnecting the supply.

Modern installations often use current-operated Residual Current Devices (RCDs) for earth fault protection, which are generally more reliable than voltage-operated ELCBs.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils, checks attendance, and reviews the previous lesson briefly. The teacher then asks pupils what they think protects electrical appliances from getting damaged when there is too much current or a short circuit. The teacher introduces the topic “Circuit Breaker”.
Pupils’ Activity: Pupils respond to questions and listen attentively. They state what they think protects electrical appliances.
Learning Point: Pupils are prepared for the new lesson and link it to prior knowledge.

Step 2: Meaning of Circuit Breaker

Time: 8 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher displays a sample circuit breaker and defines what a circuit breaker is. The teacher explains its primary function as an automatic switch for protection.
Pupils’ Activity: Pupils observe the circuit breaker sample and listen to the explanation. They write down the definition.
Learning Point: Pupils understand the basic definition and purpose of a circuit breaker.

Step 3: Functions of Circuit Breakers

Time: 7 minutes
Teaching Skill: Elucidation/Discussion
Teacher’s Activity: The teacher explains the various functions of circuit breakers, emphasizing their role in safety and protection. The teacher encourages pupils to mention situations where a circuit breaker would be useful.
Pupils’ Activity: Pupils listen, ask questions, and contribute ideas on the uses of circuit breakers.
Learning Point: Pupils grasp the importance and practical applications of circuit breakers.

Step 4: Types of Circuit Breakers

Time: 8 minutes
Teaching Skill: Listing/Classification
Teacher’s Activity: The teacher introduces the general classification of circuit breakers and then focuses on current operated and voltage operated types. The teacher shows diagrams or different samples if available.
Pupils’ Activity: Pupils listen and take notes on the different types of circuit breakers.
Learning Point: Pupils can identify and list various types of circuit breakers.

Step 5: Current Operated Circuit Breaker

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher explains the working principle of a current operated circuit breaker, focusing on how it detects overcurrents and trips to protect the circuit.
Pupils’ Activity: Pupils listen and ask questions for clarification. They note down the explanation.
Learning Point: Pupils understand how current operated circuit breakers function.

Step 6: Voltage Operated Circuit Breaker

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher explains the working principle of a voltage operated circuit breaker, highlighting its role in detecting earth faults by monitoring voltage differences. The teacher may compare it briefly with current-operated RCDs.
Pupils’ Activity: Pupils listen and compare the operating principles with current operated types.
Learning Point: Pupils understand how voltage operated circuit breakers function for earth fault protection.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define a circuit breaker.
State three functions of a circuit breaker.
Mention two types of circuit breakers based on their operation.
Briefly explain how a current operated circuit breaker works.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the importance of circuit breakers for safety. The teacher gives an assignment: “Draw and label a simple diagram of a Miniature Circuit Breaker (MCB).”
Pupils’ Activity: Pupils listen to the summary and copy the assignment.
Learning Point: Pupils consolidate their learning and prepare for further study.

Lesson Keywords

Circuit Breaker – An automatic switch that protects an electrical circuit from overcurrent damage.
Overcurrent – A current exceeding the normal or rated current of a circuit or device.
Short Circuit – An abnormal connection between two nodes of an electrical circuit intended to be at different voltages, resulting in a large current.
Current Operated – A device that responds to the magnitude of current flowing through it.
Voltage Operated – A device that responds to the magnitude of voltage across certain points.

Differentiation

For pupils who grasp concepts quickly, the teacher can ask them to research the differences between MCBs and MCCBs. For pupils needing more support, the teacher will provide simplified diagrams and re-explain concepts using more practical examples, encouraging peer support.

Note for teachers using this lesson plan

Teachers should ensure they have working samples or clear diagrams of circuit breakers for effective demonstration. Emphasize the safety aspects of circuit breakers throughout the lesson. Encourage pupils to ask questions and share any experiences they might have had with circuit breakers at home or in school.